Light-emitting element display device

ABSTRACT

A light-emitting element display device includes a substrate, one or a plurality of thin film transistors, a light-emitting element, a first electrode, and a second electrode. The substrate includes an insulating material. The thin film transistors are in each pixel of a display area on the substrate. The light-emitting element emits light by current flow in each pixel. The first electrode is between the substrate and the thin film transistors, and overlaps at least two of the thin film transistors when viewed in plan. The second electrode includes a conducting material, and is arranged across the first electrode from the substrate via an insulating film so as to form a capacitor together with the first electrode.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.14/598,945, filed on Jan. 16, 2015, which claims priority from Japaneseapplication JP2014-007295 filed on Jan. 17, 2014, the entire contents ofwhich are hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light-emitting element displaydevice.

2. Description of the Related Art

In recent years, light-emitting element display devices includingself-luminous elements, such as organic light-emitting diodes (OLEDs),have been in practical use. An organic electro-luminescent (EL) displaydevice, including such a self-luminous OLED, is excellent in visibilityand response speed compared with liquid crystal display devices known inthe art. Additionally, such a self-luminous OLED eliminates the need foran auxiliary lighting device, such as a backlight, from display devices,and allows them to be thinner.

JP 4989415 B discloses an organic EL display device including thin filmtransistors and capacitors that compensate for a threshold voltage of adriver transistor arranged in each pixel.

Recent increases in definition of light-emitting element displaydevices, such as the organic EL display devices described above, haveled to decreases in their pixel size. Such an organic EL display devicecontrols current in each pixel by holding a potential differencecorresponding to a grayscale value of the pixel. A decrease in the sizeof the pixel, which causes a decrease in the size of the correspondingelectrode, results in a decrease in a capacitance for holding thepotential difference. When the capacitance for holding the potentialdifference is small, noise or a weak leakage current may change thepotential difference, and thus cause uneven brightness across differentpixel positions. This may result in deterioration in the displayquality.

SUMMARY OF THE INVENTION

The present invention has been made with the above circumstances inmind, and it is an object of the invention to provide a light-emittingelement display device that keeps its display quality high even with itsdefinition increased.

A light-emitting element display device according to an aspect of thepresent invention includes a substrate, a plurality of pixels, one or aplurality of thin film transistors, a light-emitting element, a firstelectrode, and a second electrode. The substrate is made of aninsulating material. The pixels are in a display area on the substrate.The thin film transistors are in each of the pixels. The light-emittingelement emits light by current flow in each of the pixels . The firstelectrode is between the substrate and the thin film transistors, andoverlaps at least two of the thin film transistors when viewed in plan.The second electrode is made of a conducting material, and arrangedacross the first electrode from the substrate via an insulating film soas to form a capacitor together with the first electrode. Here, “pixel”means a unit including a light-emitting element. When a pixel is made upof a plurality of sub-pixels each including a light-emitting element,each sub-pixel corresponds to “pixel”.

In the light-emitting element display device according to the aspect,the first electrode may be across the plurality of pixels, or the firstelectrode may be across the display area. In this case, the firstelectrode may include slits, which are holes in a plurality of portionsof the first electrode when viewed in plan.

In the light-emitting element display device according to the aspect,the first electrode may be connected to a reference potential for havingthe light-emitting element emit light in each of the pixels.

In the light-emitting element display device according to the aspect,the first electrode may be electrically connected to a cathode electrodeof the light-emitting element, and the second electrode may beelectrically connected to an anode electrode of the light-emittingelement.

In the light-emitting element display device according to the aspect,each of the pixels may have a pixel transistor for controllingapplication of a voltage corresponding to a grayscale value, and adriver transistor for controlling light emission based on a potentialapplied through the pixel transistor. The second electrode may beconnected to a gate of the driver transistor.

In the light-emitting element display device according to the aspect,the first electrode may be connected to any one of a source and drain ofthe driver transistor.

The light-emitting element display device according to the aspect mayfurther include a third electrode made of a conducting material, whichis arranged across the second electrode from the substrate via aninsulating film so as to form a capacitor together with the secondelectrode. The third electrode may be electrically connected to thefirst electrode so as to form a capacitor together with the secondelectrode.

The light-emitting element display device according to the aspect mayfurther include a third electrode made of a conducting material, whichis arranged across the second electrode from the substrate via aninsulating film so as to form a capacitor together with the secondelectrode. The first electrode may be connected to the cathode electrodeof the light-emitting element. The second electrode may be connected toany one of a source and drain of the driver transistor. The thirdelectrode may be connected to a gate of the driver transistor.

A light-emitting element display device according to another aspect ofthe present invention includes a substrate, a plurality of pixels, oneor a plurality of thin film transistors, a light-emitting element, afirst electrode, and a second electrode. The substrate is made of aninsulating material. The pixels are in a display area on the substrate.The thin film transistors are in each of the pixels. The light-emittingelement includes an organic layer including a light-emitting layer, ananode electrode, and a cathode electrode. The first electrode is betweenthe substrate and the thin film transistors, and overlaps at least twoof the thin film transistors when viewed in plan. The second electrodeis arranged across the first electrode from the substrate via aninsulating film, and is opposite the first electrode.

A light-emitting element display device according to still anotheraspect of the present invention includes a substrate, a plurality ofpixels, one or a plurality of thin film transistors, a light-emittingelement, a second semiconductor layer, a first electrode, and a secondelectrode. The substrate is made of an insulating material. The pixelsare in a display area on the substrate. The thin film transistors are ineach of the plurality of pixels, and have a first semiconductor layer.The light-emitting element includes an organic layer including alight-emitting layer, an anode electrode, and a cathode electrode. Thesecond semiconductor layer is in a layer identical to the firstsemiconductor layer. The first electrode is between the substrate andthe thin film transistors. The second electrode is arranged across thefirst electrode from the substrate via an insulating film, and isopposite the first electrode. The first electrode overlaps the secondsemiconductor layer and the first semiconductor layer of at least one ofthe thin film transistors when viewed in plan.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing an organic EL display deviceaccording to an embodiment of the present invention;

FIG. 2 is a diagram schematically showing a cross section taken alongline II-II in FIG. 1;

FIG. 3 is a diagram showing an example of an organic EL display devicewithout a counter substrate;

FIG. 4 is a diagram showing an example arrangement of sub-pixelsincluded in the pixel shown in FIG. 1;

FIG. 5 is a diagram showing another example arrangement of sub-pixelsincluded in the pixel shown in FIG. 1;

FIG. 6 is a circuit diagram showing an example of a circuit in thesub-pixel;

FIG. 7 is a diagram showing a cross section taken along line VII-VII inFIG. 4;

FIG. 8 is a cross-sectional view showing a first modification of theembodiment when viewed from the same direction as FIG. 7;

FIG. 9 is a diagram schematically showing an arrangement of first andsecond electrodes according to the first modification shown in FIG. 8,when viewed in plan;

FIG. 10 is a cross-sectional view showing a second modification of theembodiment;

FIG. 11 is a cross-sectional view showing a third modification of theembodiment; and

FIG. 12 is a cross-sectional view showing a fourth modification of theembodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described below withreference to the accompanying drawings. The disclosure herein is merelyan example, and any modification coming within the spirit of the presentinvention and obvious to those skilled in the art is intended to beincluded within the scope of the invention as a matter of course. Theaccompanying drawings schematically illustrate widths, thicknesses,shapes, or other characteristics of each part for clarity ofillustration, compared to actual configurations. However, such aschematic illustration is merely an example and not intended to limitthe present invention. In the present specification and drawings, someelements identical or similar to those shown previously are denoted bythe same reference signs as the previously shown elements, and thusrepetitive detailed descriptions of them may be omitted as appropriate.

FIG. 1 schematically shows an organic EL display device 100 that is alight-emitting element display device according to an embodiment of thepresent invention. As shown in the figure, the organic EL display device100 includes a thin film transistor (TFT) substrate 120, a countersubstrate 150, and a transparent resin filler 191 (see FIG. 2) sealedbetween these two substrates. A display area 205 including pixels 210arranged in a matrix is formed on the TFT substrate 120 and countersubstrate 150 of the organic EL display device 100. Each pixel 210includes a plurality of sub-pixels 212 described below.

The TFT substrate 120 is a substrate including a transparent glass or aresin insulation material. A driver integrated circuit (IC) 182 isdisposed on the TFT substrate 120. The driver IC 182 applies a potentialfor conducting between the source and drain of a TFT (pixel transistor220 described below) arranged in each sub-pixel 212 to the correspondingscan line 262, and applies a voltage corresponding to a grayscale valueof each sub-pixel 212 to the corresponding data line 261 describedbelow. A flexible printed circuit (FPC) 181 is mounted on the TFTsubstrate 120. The FPC 181 inputs external signals including imagesignals. As indicated by the arrow in the figure, the organic EL displaydevice in this embodiment is a top-emitting organic EL display devicethat emits light toward a light-emitting layer side of the TFT substrate120.

FIG. 2 is a diagram schematically showing a cross section taken alongline II-II in FIG. 1. As shown in this cross-sectional view, the TFTsubstrate 120 includes a TFT circuit layer 160, a plurality of organicEL elements 130, and a sealing film 125. TFT circuit layer 160 includesa TFT circuit. The organic EL elements 130 are a plurality oflight-emitting elements formed on the TFT circuit layer 160. The sealingfilm 125 covers the organic EL elements 130 to block moisture. As manyorganic EL elements 130 as the sub-pixels 212 are formed in each pixel210, which is briefly shown in FIG. 2 for clarity of illustration. Acolor filter and a black matrix are formed on the counter substrate 150.The color filter allows light with different wavelength regions, forexample, three or four colors of light to pass through it. The blackmatrix is a light-blocking film that blocks light emitted from theboundaries between the sub-pixels 212. The filler 191 sandwiched betweenthe TFT substrate 120 and the counter substrate 150 is sealed by asealant 192.

Whereas the organic EL display device 100 in this embodiment includesthe counter substrate 150 as shown in FIG. 2, the organic EL displaydevice 100 can be configured without the counter substrate 150 as shownin FIG. 3. As also shown in FIG. 3, the driver IC 182 may be arranged onthe FPC 181. Especially when the TFT substrate 120 is made of a flexibleresin material, the TFT substrate 120 may be integrated with the FPC181. Whereas the organic EL element 130 in this embodiment emits whitelight and the color filter allows the light with three or four colors ofwavelength regions to pass through it, the organic EL element 130 mayemit light with different wavelength regions, for example, three or fourcolors of light.

FIG. 4 is a diagram showing an example arrangement of the sub-pixels 212included in the pixel shown in FIG. 1. As shown in the diagram, thepixel 210 includes the sub-pixels 212 each being substantiallyrectangular and emitting light with any one of the wavelength regionscorresponding to four colors: red (R), green (G), blue (B), and white(W). The sub-pixels 212 within the same pixel 210 are arranged in atwo-by-two matrix so that two sides of each sub-pixel 212 are in contactwith the adjoining sub-pixels 212. The arrangement of the sub-pixels 212within the pixel 210 is not limited to the arrangement shown in FIG. 4.Alternatively, the pixel 210 may include the sub-pixels 212 arranged ina stripe pattern corresponding to three colors RGB as shown in FIG. 5 orin another stripe pattern corresponding to four colors RGBW. Thearrangement of the sub-pixels 212 constituting the pixel 210 is notlimited to these arrangements, and can be determined as appropriate.

FIG. 6 is a circuit diagram showing an example of a circuit in thesub-pixel 212. An operation of the circuit for light emission will bedescribed with reference to the diagram. When an image signalcorresponding to a grayscale value of each sub-pixel 212 is applied tothe data line 261, the pixel transistor 220 conducts based on a signalthrough the scan line 262. A voltage based on the grayscale value isthus stored across a capacitor 241 and/or a capacitor 242. A TFT drivertransistor 230 then passes a current based on the voltage stored acrossthe capacitor 241 and/or the capacitor 242. Thus, the organic EL element130 emits light. A capacitor 243 is located between the anode andcathode of the organic EL element 130. The cathode side of the organicEL element 130 is connected to a low reference potential VSS. The sourceside (the opposite side from the organic EL element 130) of the drivertransistor 230 is held at a high reference potential VDD.

Here, it is optional whether to form the capacitors 241, 242, and 243.All of the capacitors may be formed. Alternatively, any one or any twoof the capacitors may be formed. Whereas p-type semiconductors are usedin the circuit diagram, n-type semiconductors may be used. The circuitshown in FIG. 6 is a simplified circuit for explaining a light emissioncontrol, and thus includes two transistors. Alternatively, the circuitmay include three or more transistors, or may include other controllines and capacitors. The configuration of the circuit may be determinedoptionally.

FIG. 7 is a diagram schematically showing a cross section taken alongline VII-VII in FIG. 4. In this diagram, the filler 191 and the countersubstrate 150 are not shown and only the TFT substrate 120, the TFTcircuit layer 160, the organic EL element 130, and the sealing film 125are shown. As shown in the diagram, the TFT circuit layer 160 includesthe pixel transistor 220, the driver transistor 230, and a firstelectrode 171. The first electrode 171 is arranged between the pixeltransistor 220 and the driver transistor 230, and the TFT substrate 120.The first electrode 171 overlaps at least a portion of the drivertransistor 230 and at least a portion of the pixel transistor 220 whenviewed in plan. A second electrode 172 is arranged across the firstelectrode 171 from the TFT substrate 120, here between the pixeltransistor 220 and the driver transistor 230, and the first electrode171. The second electrode 172 thus forms a capacitor together with thefirst electrode 171 via an insulating film 163. In this embodiment, thefirst electrode 171 is formed covering the plurality of sub-pixels 212and the display area 205, and overlapping the display area 205, whenviewed in plan.

Here, the first electrode 171 can be made of a metal containing at leastany one of molybdenum (Mo) and tungsten (W), and can be a solidelectrode that covers the display area 205. Use of a refractory metal,such as a metal containing MO or W, can prevent degradation of theelectrode caused by melting or the like even in a heating process duringmanufacture, and maintain quality. This is effective especially when asemiconductor layer 224 or 234 is made of polysilicon or othersemiconductors. The second electrode 172 can also be made of arefractory metal containing at least any one of Mo and W. This alsoproduces similar effects. Use of a high-dielectric material, such asSiN, in the insulating film 163 can increase the electric capacitance ofthe capacitor formed by the first electrode 171 and the second electrode172. The second electrodes 172 are separately formed correspondingone-to-one to the sub-pixels 212, and connected to the circuits in thesub-pixels 212. An underlayer 161 made of SiNx or other insulatingmaterials is formed between the first electrode 171 and the TFTsubstrate 120.

The driver transistor 230 includes a gate 231, a source 232, and a drain233. A semiconductor layer 234 is arranged between the source 232 andthe drain 233. The pixel transistor 220 includes a gate 221, a source223, and a drain 222. A semiconductor layer 224 is arranged between thesource 223 and the drain 222. The drain 222 of the pixel transistor 220and the gate 231 of the driver transistor 230 are connected to eachother. An insulating film 166 made of SiNx or other insulating materialsis formed between the semiconductor layers 224 and 234, and the gates221 and 223. An insulating film 167 made of SiNx or other insulatingmaterials is formed on the gates 221 and 231. A planarization film 168made of an organic insulating material is formed on the pixel transistor220 and the driver transistor 230.

The organic EL element 130 includes an anode electrode 131, aninter-pixel insulating film 135, an organic layer 132, and a cathodeelectrode 133. The anode electrode 131 is connected to the drain 233 ofthe driver transistor 230 through a contact hole in the planarizationfilm 168. The inter-pixel insulating film 135 covers the edge of theanode electrode 131 with an organic insulating material to insulate theanode electrode 131 from the anode electrode 131 of the adjacentsub-pixel 212. The organic layer 132 is formed in contact with the anodeelectrode 131 of each sub-pixel 212 so as to cover the display area 205.The cathode electrode 133 is a transparent conductive film made of acomposite oxide of indium and tin, a composite oxide of indium and zinc,or other composite oxides. A light-emitting area LEA is the area wherethe anode electrode 131 is in contact with the organic layer 132.

In the configuration as described above, the first electrode 171 isconnected to the source 232 of the driver transistor 230, and connectedto the high reference potential VDD at a plurality of portions outsidethe display area 205 to be maintained at the high reference potentialVDD. The second electrode 172 is connected to the gate 231 of the drivertransistor 230 (i.e., the drain 222 of the pixel transistor 220) . Thefirst electrode 171 and the second electrode 172 thus form the capacitor241 shown in the circuit diagram of FIG. 6. The first electrode 171 andthe second electrode 172 form the capacitor 241 with high capacitance,and thus can stabilize current provided to the organic EL element 130.Such capacitor can be formed without affecting the circuit configurationbecause the first electrode 171 and the second electrode 172 are formednear the TFT substrate 120 side of the driver transistor 230 and pixeltransistor 220. The first electrode 171 is connected to the highreference potential VDD and formed overlapping the display area 205, andthus can more evenly provide the high reference potential VDD to thedisplay area 205. In addition, the first electrode 171 eliminates theneed for another line for providing the high reference potential VDDwithin the circuit in the each sub-pixel 212, and thus allows the drivertransistor 230 or the pixel transistor 220 to be larger. Connecting thefirst electrode 171 to the high reference potential VDD at a pluralityof portions outside the display area 205 can provide the first electrode171 with more stable potential. The first electrode 171 is formedoverlapping the display area 205. This configuration can efficientlydissipate heat generated in the organic EL element 130 and shieldelectromagnetic noise generated in the circuits.

In the embodiment described above, the first electrode 171 is connectedto the source 232 of the driver transistor 230 and the second electrode172 is connected to the gate 231 of the driver transistor 230.Alternatively, the first electrode 171 may be connected to the lowreference potential VSS, to which the cathode electrode of the organicEL element 130 is connected, that is, to the cathode electrode of theorganic EL element 130, in the display area 205. In addition to this,the second electrode 172 may be connected to the drain 233 of the drivertransistor 230, that is, to the anode electrode of the organic ELelement 130. Such alternative configuration can also form the capacitor243.

FIG. 8 is a cross-sectional view showing a first modification of theembodiment described above when viewed from the same direction as FIG.7. In the embodiment described above, the first electrode 171 is a solidelectrode that covers the display area 205. By contrast, the firstmodification differs from the embodiment in that a slit 178, a hole, isformed in a portion of the first electrode 171. FIG. 9 is a diagramschematically showing an arrangement of the first electrode 171 and thesecond electrode 172 when viewed in plan. As shown in the diagram, thesecond electrodes 172 are separately arranged corresponding one-to-oneto the sub-pixels 212 so as to overlap the first electrode 171 thatoverlaps the entirety of the display area 205. The slits 178 in thefirst electrode 171 are disposed in portions that does not overlap thesecond electrodes 172 so that the first electrode 171 forms acapacitance together with the second electrodes 172. The first electrode171 is electrically connected to a plurality of terminals 185 outsidethe display area 205, and maintained at the high reference potentialVDD.

Such configuration can relieve stress that occurs in the first electrode171 and efficiently dissipate heat, in addition to the effects accordingto the embodiment described above. Whereas the slit 178 is formed in ahole shape in FIG. 8, the slit 178 may extend across the first electrode171 so as to cut it. Also in such a case, each first electrode 171 isformed to overlap at least a portion of the driver transistor 230 and atleast a portion of the pixel transistor 220 when viewed in plan, andconnected to a fixed potential, such as the high reference potentialVDD.

FIG. 10 is a cross-sectional view showing a second modification of theembodiment described above. Unlike FIG. 7, this cross-sectional viewshows a cross section of a portion where no pixel transistors 220 areformed. As shown in the cross-sectional view, the second electrode 172is formed using a layer identical to any of a plurality of layersconstituting TFTs, in a portion where no pixel transistor 220 areformed. As shown especially in FIG. 10, the second electrode 172 isformed using the layer identical to the semiconductor layer 234. Thus,the second electrode 172 can be used as a conductor by, for example,changing the amount of ions implanted to the semiconductor layer 234made of low-temperature polysilicon. Alternatively, the second electrode172 may be formed using a conducting layer including source and drainelectrodes.

Here, the slit 178 vertically and horizontally extends across the firstelectrode 171 when viewed in plan to form electrodes electricallyseparated for each sub-pixel 212. However, the first electrodes 171electrically separated for each sub-pixel 212 are arranged to overlap atleast a portion of the pixel transistor 220 and at least a portion ofthe driver transistor 230 when viewed in plan. The first electrode 171is connected to the drain 233 of the driver transistor 230, and thesecond electrode 172 is connected to the gate 231 of the drivertransistor 230 via a bridge 174 made of a conductor. Thus, the firstelectrode 171 and the second electrode 172 form the capacitor 242 shownin FIG. 6.

The first electrode 171 and the second electrode 172 according to thesecond modification also form the capacitor 242 with high capacitance,and thus can stabilize current provided to the organic EL element 130.Such capacitor can be formed without affecting the circuit configurationbecause the first electrode 171 and the second electrode 172 are formedoverlapping transistors. Furthermore, the first electrode 171 and thesecond electrode 172 can efficiently dissipate heat generated in theorganic EL element 130 and shield electromagnetic noise generated in thecircuits.

FIG. 11 is a cross-sectional view showing a third modification of theembodiment described above. Like the second modification, thiscross-sectional view shows a cross section of a portion where no pixeltransistors 220 are formed. As shown in the cross-sectional view, theTFT circuit layer 160 includes a third electrode 173 as well as thefirst electrode 171 and the second electrode 172. The first electrode171 and the second electrode 172 are arranged between the drivertransistor 230 and the pixel transistor 220, and the TFT substrate 120.The first electrode 171 overlaps at least a portion of the drivertransistor 230 and at least a portion of the pixel transistor 220. Thethird electrode 173 is formed using a layer identical to any of aplurality of layers constituting transistors, in a portion where nopixel transistor 220 are formed. In FIG. 11, the third electrode 173 isformed using the layer identical to the semiconductor layer 234. Thus,the third electrode 173 can be used as a conductor by changing, forexample, the amount of ions implanted to the semiconductor layer 234made of low-temperature polysilicon, like the second modification.Alternatively, the third electrode 173 may be formed using a conductinglayer including source and drain electrodes. Here, the first electrode171 and the second electrode 172 can be made of a refractory metalcontaining at least any one of Mo and W.

The first electrode 171 and the third electrode 173 are electricallyconnected to each other, and overlap each other so as to sandwich thesecond electrode 172 between them. This configuration increases acapacitance formed between the first electrode 171 and the thirdelectrode 173, and the second electrode 172. Here, the second electrode172 is connected to the source 232 of the driver transistor 230, and thefirst electrode 171 and the third electrode 173 are connected to thegate 231 of the driver transistor 230. Thus, the first electrode 171 andthe third electrode 173, and the second electrode 172 form the capacitor241 shown in FIG. 6.

The first electrode 171 and the second electrode 172 according to thethird modification also form the capacitor 241 with high capacitance,and thus can stabilize current provided to the organic EL element 130.Such higher capacitor can be formed without affecting the circuitconfiguration because the first electrode 171 and the second electrode172 are formed overlapping transistors. Furthermore, the first electrode171 and the second electrode 172 can efficiently dissipate heatgenerated in the organic EL element 130 and shield electromagnetic noisegenerated in the circuits.

FIG. 12 is a cross-sectional view showing a fourth modification of theembodiment described above. The fourth modification includes the firstelectrode 171, the second electrode 172, and the third electrode 173like the third modification, but differs from the third modification inthat the first electrode 171 is not electrically connected to the thirdelectrode 173. In such a case, for example, the first electrode 171 isconnected to the low reference potential VSS identical to the potentialof the cathode electrode 133, and third electrode 173 is connected tothe gate 231 of the driver transistor 230 via the bridge 174. Thisconfiguration can form the capacitors 242 and 243 shown in FIG. 6. Theconfiguration can form high capacitance more efficiently, stabilizepotential, and thus improve display quality.

While there have been described what are at present considered to becertain embodiments of the invention, it will be understood that variousmodifications may be made thereto, and it is intended that the appendedclaims coverall such modifications as fall within the true spirit andscope of the invention.

What is claimed is:
 1. A light emitting element display devicecomprising: a substrate; a plurality of pixels in a display area on thesubstrate; a plurality of thin film transistors in each of the pluralityof pixels; a light emitting element in each of the pixels; and acapacitor including: a first electrode which is arranged between thesubstrate and a semiconductor layer of one of the plurality of thin filmtransistor and overlaps with the semiconductor layer in plan view; and asecond electrode between the first electrode and the semiconductorlayer.
 2. The light emitting element display device according to claim1, wherein the plurality of thin film transistors in each of theplurality of pixels includes: a pixel transistor controlling input of anapplied voltage corresponding to a grayscale value to the capacitor; anda driver transistor controlling light emission based on the appliedvoltage, and wherein the second electrode is coupled to a gate of thedriver transistor.
 3. The light emitting element display deviceaccording to claim 2, wherein the first electrode is coupled to one of asource and a drain of the driver transistor.
 4. The light emittingelement display device according to claim 1, wherein the light emittingelement includes: an anode; an organic electroluminescence layerconnected to the anode; and a cathode connected on the organicelectroluminescence layer, wherein the first electrode is coupled to thecathode, and the second electrode is coupled to the anode.
 5. The lightemitting element display device according to claim 1, wherein the firstelectrode spreads over two or more of the plurality of pixels.
 6. Thelight emitting element display device according to claim 1, wherein thefirst electrode is coupled to a reference potential.
 7. The lightemitting element display device according to claim 1, further comprisinga third electrode which is arranged on the second electrode and iscoupled to the first electrode so as to form the capacitor together withthe second electrode.
 8. The light emitting element display deviceaccording to claim 2, wherein each of the pixel transistor and thedriver transistor overlaps with the first and the second electrodes. 9.A light emitting element display device comprising: a substrate; aplurality of pixels in a display area on the substrate; a plurality ofthin film transistors in each of the plurality of pixels; a lightemitting element in each of the pixels; and a capacitor including: asemiconductor layer of one of the plurality of thin film transistors;and a first electrode which is arranged between the substrate and thesemiconductor layer and overlaps with the semiconductor layer in planview.
 10. The light emitting element display device according to claim9, wherein the plurality of thin film transistors in each of theplurality of pixels includes: a pixel transistor controlling input of anapplied voltage corresponding to a grayscale value to the capacitor; anda driver transistor controlling light emission based on the appliedvoltage, and wherein the semiconductor layer is coupled to a gate of thedriver transistor.
 11. The light emitting element display deviceaccording to claim 10, wherein the first electrode is coupled to one ofa source and a drain of the driver transistor.
 12. The light emittingelement display device according to claim 9, further comprising anothercapacitor including: a second electrode between the first electrode andthe substrate; and the first electrode.
 13. The light emitting elementdisplay device according to claim 12, wherein the light emitting elementincludes: an anode; an organic electroluminescence layer connected tothe anode; and a cathode connected on the organic electroluminescencelayer, wherein the first electrode is coupled to the anode, and thesecond electrode is coupled to the cathode.
 14. A light emitting elementdisplay device comprising: a substrate; a plurality of pixels in adisplay area on the substrate; a plurality of thin film transistors ineach of the plurality of pixels; a light emitting element in each of thepixels; and a capacitor including: a first electrode which is arrangedbetween the substrate and a conductive layer of one of the plurality ofthin film transistor and overlaps with the conductive layer in planview; and a second electrode between the first electrode and theconductive layer.
 15. The light emitting element display deviceaccording to claim 14, further comprising another capacitor including: asemiconductor layer which lies at a same level as the conductive layerand overlaps with the first electrode in plan view; and the firstelectrode.
 16. The light emitting element display device according toclaim 14, wherein the plurality of thin film transistor in each of theplurality of pixels includes: a pixel transistor controlling input of anapplied voltage corresponding to a grayscale value to the capacitor; anda driver transistor controlling light emission based on the appliedvoltage, and wherein the second electrode is coupled to one of a sourceand a drain of the driver transistor.
 17. The light emitting elementdisplay device according to claim 16, wherein the light emitting elementincludes: an anode; an organic electroluminescence layer connected tothe anode; and a cathode connected on the organic electroluminescencelayer, wherein the first electrode is coupled to the cathode, and thesecond electrode is coupled to the anode.